Electronic and forensics experts say information could be pulled from computers seized from Lanza's Newtown home, even if they were struck with a hammer, as some reports say.

"If he drilled holes into it, that would be a different story," said Mark Morton, a laboratory supervisor in the University of New Haven's electrical engineering department. "It depends on how much the federal government wants to spend. I believe if the federal government wants to recover data, it will get the data."

Morton said techniques to recover data from severely damaged computers include dismantling and reassembling hard-drive pieces or using software owned by the Department of Defense.

Peter Valentin, a retired State Police detective and forensics expert, said the FBI and the Defense Department would have the expertise to extract data.

"If the hard drives were physically damaged, it's a tougher proposition ... but I wouldn't say it's impossible," he said.

"Clearly a lot of effort will be spent trying to see what's on the hard drives," said Valentin, now a University of New Haven professor of forensic science. "It certainly could be a treasure trove."

Sources have said the state police are heading the shooting investigation.

For much of the past week, their detectives and forensic experts have been reconstructing the crime scene inside the Sandy Hook school trying to pinpoint Lanza's movements and determine when and where he shot each victim.

Lanza burst into the school by shooting his way through the locked front door. He then used a military-style Bushmaster .223 semiautomatic rifle to murder the principal and school psychologist as they ran to confront him. He walked down the hallway and into two first-grade classrooms, killing six adults and 20 students.

Upon hearing police sirens and officers smashing windows to enter the school, Lanza ducked into another room and committed suicide with one of the two handguns he carried, a source said.

Sources said hundreds of rounds of unused ammunition were found, leading them to believe Lanza would have continued his killing spree had police not arrived when they did.

Expelled casings, bullet trajectories, embedded fragments and blood splatter have been diagrammed in the hallway and the classrooms by investigators. Evidence including the guns used as well as fingerprints and DNA found have been sent to the state's forensic laboratory.

Valentin said evidence found in the car Lanza drove to the school also could be important to the probe.

"There could be papers, notes, receipts, a backpack, a lot of personal material, particularly if that car was used by him often," the retired police detective said.

The car was owned by Nancy Lanza, the killer's mother. She was found dead in her bed with four .22-caliber bullet wounds in the face, a source said. A hunting rifle found at the home is believed to have been used in that murder. All of the guns found were legally purchased by Lanza's mother, who often took her son to shooting ranges.

Valentin said Newtown police are "a very important source of background information," particularly if they had any prior contact with the Lanzas.

A number of federal agencies are working with the State Police.

Agents from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives have been investigating where Lanza's weapons and ammunition were bought and at which ranges they were fired.

FBI agents have been involved in the interview process, crime-scene recovery, forensic assistance, record requests and document production.

Often, the U.S. Secret Service is involved in credit-card investigations, while the Department of Defense has reconstructed computer hard drives damaged in explosions or by terrorism suspects.

Sources said the federal agencies would be instrumental in obtaining information from Microsoft, Sony and other companies that operate online video gaming sites requiring people pay to play.

Microsoft requires its Xbox 360 owners and Sony requires PlayStation fans to purchase subscriptions to play online. Those subscriptions often are bought with a credit card and require the individual's name, screen name and an email address.

"I would think that information is available," said Valentin, who as a state police detective investigated hundreds of cases, including the 2009 Yale University murder of Annie Le. The doctoral student's body was found stuffed behind a basement wall and her lab technician killer pleaded guilty and was sentenced to 44 years in prison.

Valentin said once investigators determine Lanza's game-playing user or screen names, they could determine what games, days and times he played online. They could then try to locate gamers who played with him.

"You could ask hosts to check their database for screen names," he said.

They could use Lanza's email account to subpoena mail he sent and received and identify people with whom he corresponded.

All could be questioned.

Beyond attempts to recover data from the hard drive, Valentin said there's the possibility Lanza stored information in the cloud, a virtual hard drive that users access from the Internet.

He said cloud technology negates the need for portable hard drives and thumb drives, which also may have been found in the house.

Cell phones seized at the Lanza home also may contain contacts, text messages and email correspondence that could prove useful, Valentin said.

Medical records could show not only whether Lanza ever saw a therapist but also treatment dates, prescribed medications and any issues he may have had. Some of those records have been obtained and are being reviewed by the state police, according to a Hartford Courant report.

"I don't think the medical component alone will make us understand what happened," Valentin said.

He expects the full investigative report will take several months to complete.